The direct reduction of iron ore requires the production of a synthesis gas or reducing gas containing hydrogen and carbon monoxide for reaction with the iron ore in the shaft furnace. Numerous processes have been used or proposed for the production of a synthesis gas containing hydrogen and carbon monoxide. Among these processes are the following.
U.S. Pat. No. 3,828,474 discloses a process for the production of a high strength reducing gas suitable for reducing metallic ores such as iron ore. The process disclosed is a multi-step process using a C.sub.3 to C.sub.15 hydrocarbon such as liquid naphtha as the starting material. The first step of the process disclosed comprises gasifying the hydrocarbon by passing a preheated mixture of the hydrocarbon and steam through a bed of a reforming catalyst to produce a gas consisting essentially of methane, hydrogen, carbon oxides and steam. Carbon dioxide is removed from this gas mixture and the resulting gas is further reformed in the presence of a reforming catalyst to produce a gas comprising hydrogen and carbon monoxide.
U.K. Pat. No. 1,270,071 discloses a process for the production of a reducing gas. In the process disclosed, a steam reforming effluent having a total concentration of carbon monoxide and hydrogen of at least 80 mole percent is produced by effecting the steam reforming in at least two zones, with a portion of the hydrocarbon feed being introduced into the first zone and the remaining portion of the hydrocarbon feed being introduced into the subsequent zone(s). Also in the process, the effluent of each zone, including the first zone, is admixed with the portion of the feed to be introduced into the subsequent zone for the completion of the steam reforming. The temperature of the mixing is regulated such that the temperature of the mixture being introduced into the subsequent zone(s) is at least 1200.degree. F. The steam requirements are regulated to provide a steam to carbon ratio into the second and subsequent zone(s) of less than 2:1 and a steam to carbon ratio for the first zone of at least 2:1. A similar process is disclosed in a German article by H. Jockel et al entitled: "Manufacture of Reduction Gas for Ore Smelting by Two-Stage Catalytic Steam Reforming of Natural Gas" (Abstract in English).
U.K. Pat. No. 1,398,078 discloses a process for producing a reducing gas by reforming a hydrocarbon feedstock in a first stage with an excess of steam in a catalyst bed externally heated in a furnace to give a reformer gas containing carbon oxides, hydrogen, unreacted steam, and possibly hydrocarbons, cooling the reformer gas, condensing and removing at least a portion of the unreacted steam. In the second stage, reheating the dried reformer gas to a temperature in the range of 750.degree.-1100.degree. C. and reacting the carbon dioxide and the steam in the gas with any hydrocarbons contained therein or added thereto.
U.K. Pat. No. 1,569,014 discloses a process for producing a synthesis gas by first desulfurizing and dividing into two fractions a hydrocarbon feedstock. The first fraction undergoes a primary steam reforming reaction at high pressure and mild temperature. The gas effluent from said reaction, as well as the second fraction of the feedstock, subsequently undergo jointly a secondary reforming reaction in an adiabatic reactor, by reacting with an oxygen containing gas. A similar process is proposed in an article by E. Supp in the July 1984 issue of Hydrocarbon Processing entitled "Convert Methanol Economically".
U.K. Pat. Appln. No. 2,153,383A discloses a process for producing a reducing gas having a high reduction potential. In the process, the reducing gas is prepared by catalytic conversion in two steps of a sulfur-free gas mixture of hydrocarbons having a high content of hydrocarbons with two or more carbon atoms. In the first step of the process, an inlet stream of at least a part of the gas mixture together with added steam is passed through an adiabatic reactor containing a steam reforming catalyst at an inlet temperature of 400.degree.-550.degree. C. and an outlet temperature of 400.degree.-500.degree. C. and at a pressure of 1-30 kg/cm.sup.2 g, the amount of steam added being calculated for obtaining in the inlet stream an H/C ratio of at least 4.8 and an O/C ratio of between 0.5 and 1. The outlet stream from the first step is combined with the top-gas from a reduction furnace, and the combined stream in then further converted in a second step by steam reforming.
As with reducing gas production processes, there are numerous process configurations which are in use or have been proposed for the direct reduction of iron ore. Patent and publications which are representative of these are U.S. Pat. Nos. 4,439,233; 3,764,123 and 3,423,201 and and article by Robert Lawrence in the Feb. 22, 1971 edition of Chemical Engineering entitled "Direct Reduction Strikes While the Iron is Hot".